/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.dx.dex.code;

import com.android.dx.io.opcode.Opcodes;
import com.android.dx.rop.code.RegisterSpecList;
import com.android.dx.rop.code.SourcePosition;
import com.android.dx.util.AnnotatedOutput;

/**
 * Pseudo-instruction which either turns into a {@code nop} or nothingness, in
 * order to make the subsequent instruction have an even address. This is used
 * to align (subsequent) instructions that require it.
 */
public final class OddSpacer extends VariableSizeInsn {

	/**
	 * Constructs an instance. The output address of this instance is initially
	 * unknown ({@code -1}).
	 * 
	 * @param position
	 *            {@code non-null;} source position
	 */
	public OddSpacer(SourcePosition position) {
		super(position, RegisterSpecList.EMPTY);
	}

	/** {@inheritDoc} */
	@Override
	public int codeSize() {
		return (getAddress() & 1);
	}

	/** {@inheritDoc} */
	@Override
	public void writeTo(AnnotatedOutput out) {
		if (codeSize() != 0) {
			out.writeShort(InsnFormat.codeUnit(Opcodes.NOP, 0));
		}
	}

	/** {@inheritDoc} */
	@Override
	public DalvInsn withRegisters(RegisterSpecList registers) {
		return new OddSpacer(getPosition());
	}

	/** {@inheritDoc} */
	@Override
	protected String argString() {
		return null;
	}

	/** {@inheritDoc} */
	@Override
	protected String listingString0(boolean noteIndices) {
		if (codeSize() == 0) {
			return null;
		}

		return "nop // spacer";
	}
}
